Yah, I am hoping you can fix these guys, but not the way you did those guys.
Can you make them behave like troll shamans? Troll shames are solid divine casters, that function well, and are challenging. That would balance them good.
AeonBlues
An additional thought. If you can't fix these shamans, then perhaps removing them or replacing them would be better then leaving them there.
We manage to spend several rounds beating down the front line before attacking the shamans, and they still didn't fire off any thing resembling an attack. Mind you, I don't exactly give shamans a whole lot of time to get their act together, but they seem like harmless dead weight to this minotaur tribe.